A way to test things by myself?

Dota 2 is a huge, complex game with a lot of things I'd like to test. I could come in and ask but I'd rather figure it out for myself because I'm impatient haha. For instance, does Linken's Sphere block all the damage from Skywraith's Ulti or blocks only some of it? I want to test this stuff but it's pretty much impossible to test ingame or it will take way too long to find out. I watch Youtube Channels like Dotacinema and they have a thing where they can create these scenarios. Is there a mod or a way that will allow me to mess with hero's items, levels, and spells so I may test this stuff out?

All legit, of course. Don't want to get in trouble with Valve.

Dont know bout that but i can answer your query, linkin's only blocks single target point spells, so in short it doesnt block his ulti but blocks his silence and nuke.

There isnt really any need to test these things out. Pretty much all small complicated mechanics are known, and if things are different it is probably becouse it is a new hero that came out and all the small nuances from dota 1 are a bit off.

For example a lot of interactions with abbadon's ult were wrong when he came out.

As far as I know, HP Removal still heals him ._.

You can test it out in custom lobbies where you create a lobby with cheats and then do whatever you want like a sandbox.

I won't get in trouble for that?

Turning on cheats in a private lobby is on the options. You just have to tick the box.

Doing this in a private lobby has no issue to Valve, its built in. Enable cheats when going in a lobby, then use the commands found here to do your testing with. The combat log(top left of screen, one of the icons) is useful as well if you wish to go super indepth.

Test it in empty lobbies with cheat mode.
Dotacinema does this, then you find the console commands to create and level inactive bots of any hero that you can control.

Careful when testing mana costs and stuff like that, if you do don't use the -wtf cheat